A thin-walled impeller (bladed wheel), blade or the like used in a rotating machine device such as a turbine or a supercharger is manufactured through the following cutting processing steps: a difficult-to-cut alloy member (raw material) made of a Ni-based heat-resistant alloy, a stainless steel or a titanium alloy is fixed onto the rotation axis of a machine tool, then multi-axis control is performed while a cutting tool such as an endmill is being rotated and rough processing, semi-finish processing and finish processing are performed on this alloy member.
Since in the finish processing of the cutting processing steps, it is necessary to perform the finish processing such that the surface of the alloy member is curved, a ball endmill, a taper ball endmill or a radius endmill having a cutting edge formed with a peripheral cutting edge, a corner edge and a end cutting edge is conventionally used. In particular, a solid-type radius endmill (hereinafter also referred to as a “multi-flute endmill”) that has a large number of cutting edges at the tip of the main body of the tool, for example, six or more cutting edges is gradually used.
As a conventional technology on a multi-flute endmill, there is a form in which as shown in FIG. 11, a large number of cutting edges are provided, and between the adjacent cutting edges in the rotation direction R (peripheral direction) of the endmill, a gash 7 close to the center in the radial direction (rotation axis) and a flute 8 close to the periphery are provided so as to discharge chips (see Patent Document 1). FIG. 11 specifically shows an example shown in FIG. 8 of Patent Document 1.
It is thought that in the example (Patent Document 1) shown in FIG. 11, the flute 8 is formed on the backward side in the rotation direction R on the peripheral side in the radial direction of the gash 7 formed on the forward side in the rotation direction R of the end cutting edge 6, the flutes 8 are continuously formed on the gashes 7, and thus chips are unlikely to be stayed on the gashes 7, with the result that the effect of enhancing the discharge of the chips cut by the end cutting edge 6 is obtained.
An example of the endmill, other than Patent Document 1, in which the flute is formed close to the periphery in the radial direction of the gash formed close to the center in the radial direction is shown in FIG. 12 (see Patent Document 2). FIG. 12 shows FIG. 2 in Patent Document 2. In this example, chip discharge grooves 4 corresponding to the flutes in Patent Document 1 are formed continuously close to the periphery in the radial direction of the gash 7, and between the chip discharge groove 4 and the gash 7, a concave portion 10 forming the rake face 11 of a corner edge 12 is formed (paragraphs [0017] and [0018]), with the result that the gash 7 and the chip discharge groove 4 communicate with each other through the concave portion 10.
In Patent Document 2, the corner edge 12 in the shape of a segment is formed up to the start point Q of a end cutting edge 9 on the center side in the radial direction beyond the tip P of the segment, and an intersection line L that is formed from the start point Q to the back end portion side of the endmill and that partitions the concave portion 10 is located on the center side in the radial direction with respect to a straight line parallel to a center axis passing through the tip P, so that it is possible to discharge chips produced by the corner edge 12 from the rake face 11 of the cutting edge without the chips being passed around to the rake face 8 of the end cutting edge (paragraphs [0019]-[0024]).